Gasoline engines have been a dominant mode of providing propulsion for numerous types of vehicles for many years. As such, innovations aimed at improving gasoline engine performance in areas such as power and efficiency have continued to be desirable goals. A turbocharger is one example of an innovation that has improved gasoline engine performance. The turbocharger, which is sometimes referred to simply as a turbo, may be thought of as a gas compressor used to increase the mass of air entering the engine to create more engine power. As such, the turbocharger may provide forced-induction of an internal combustion engine. The turbocharger is typically driven off the engine's own exhaust gases.
On gasoline turbocharged engines, a potential problem of compressor surge exists in situations where the throttle is closed. Such situations may be particularly noticeable when the throttle is closed from an initially substantially open position. In this regard, when the throttle is closed compressed air will flow to the throttle valve, but will have no exit due to the closure of the throttle valve. The compressed air may then decompress back across the turbocharger (causing the “surge”), which may be the only path the now blocked air can take. The surge can raise the pressure of the air to a level that can cause engine damage or undesirable noise due to turbulence.
In order to prevent or at least reduce the impact of compressor surge, turbocharged engines typically include a device such as a recirculation valve. The device operates to provide a valve for permitting air between the turbocharger and the throttle valve with a flow path when the throttle valve is closed, which vents off the excess air pressure, to maintain the turbo spinning at a high speed. The air is usually recycled back into the turbocharger inlet when using a recirculation valve, but can also be vented to the atmosphere when using a blowoff valve. By providing an escape air path, engine damage and noise may be avoided as well as reduction of the phenomenon of turbo lag due to slowing down of the turbo that may take place as a result of a surge.
Although the recirculation valve or blowoff valve may be effective at preventing surge conditions, the recirculation valve otherwise does not typically provide improvement in engine power or efficiency, but still adds to cost and complexity of the engine. Accordingly, it may be desirable to provide a mechanism for avoiding use of the recirculation valve.